The present invention relates to a navigation apparatus to find a location of the vehicle.
FIG. 24 is a schematic representation of a navigation apparatus in accordance with the prior art. The block 1 is a vehicle such as a car. The block 2 is a gyro sensor to measure an angular velocity of vehicle 1. The block 3 is an engine control unit (ECU) to control an engine of vehicle 1. The block 4 is a computing unit to calculate the present location of vehicle 1 by a signal outputted from gyro sensor 2 and ECU 3.
Gyro sensor 2 is a sensor to output a value corresponding to an angular velocity (rotational angle per unit time) of the rotational motion of the wheel at the detecting direction as a voltage. There are a top type rate gyro sensor, an optical fiber gyro sensor and the like, according to detection type. These are briefly explained below.
FIG. 25 illustrates a construction of a top type rate gyro sensor. A rotor 5 rotating at a constant speed in a rotary direction 5a is supported by a gimbal 6. Gimbal 6 is supported by a spring 7 and a pick off detector 8. When a torque in a rotary direction 5a is generated at an input axis 9 of a top type rate gyro sensor, a torque is generated by a gyro effect at an output axis 10 which is orthogonal with input axis 9 and the torque is detected by pick off detector 8.
FIG. 26 illustrates a construction of an optical fiber gyro sensor. Light emitted from a laser 11 passes through fiber couplers 12 and 13 and is led in an optical fiber 14. Optical fiber 14 is several hundred meters long and is wound with a diameter of several ten millimeters. The light passing through optical fiber 14 passes through a phase modulator 15, passes through fiber couplers 12 and 13 again and is led to an optical detector 16. In an optical fiber gyro sensor thus constructed, when a torque 17 is generated around the input axis orthogonal with a winding plane of optical fiber 14, light is outputted to optical detector 16 by Sagnac effect as a variation of an optical interference.
A gyro sensor 2 for detecting an angular velocity of vehicle 1 is set in vehicle 1 so that an angular velocity around the vertical axis of vehicle 1 can be detected.
Engine control unit 3 processes information obtained from various kinds of sensors (for example, a sensor for detecting the number of rotation of the wheel) attached to vehicle 1 and controls various kinds of actions of vehicle 1. Engine control unit 3 outputs a pulse corresponding to the velocity of vehicle 1 to computing unit 4.
As shown in FIG. 27, the present location (x.sub.n, y.sub.n) of vehicle 1 is obtained by cumulatively calculating a moving distance .DELTA.D.sub.n and a moving azimuth .DELTA..theta..sub.n which vary at every period .DELTA.t from the initial location (x.sub.0, y.sub.0) at computing unit 4. The moving azimuth .theta..sub.n is obtained by integrating an angular velocity .omega..sub.n detected at gyro sensor 2 by time, where an initial azimuth at time n is defined .theta..sub.0 and period to obtain data from gyro sensor 2 is defined .DELTA.t. ##EQU1##
Then, the moving distance .DELTA.Dn of vehicle 1 is obtained by integrating a velocity v.sub.n of vehicle 1 obtained from a pulse generated at engine control unit 3, where the initial velocity is defined v.sub.0. ##EQU2##
When computing unit 4 obtains the moving distance .DELTA.D.sub.n and the moving azimuth .theta..sub.n of vehicle 1 at time n, the present location of vehicle 1 (x.sub.n, y.sub.n) is obtained by cumulative calculation from the initial location (x.sub.0, y.sub.0), as shown in FIG. 27. ##EQU3##
In the above construction, however, a velocity signal such as a pulse from engine control unit 3 of vehicle 1 is taken out to detect a moving distance of vehicle 1 and when a navigation apparatus is equiped after purchasing a vehicle, wiring work is required in vehicle 1. It is sometimes impossible to connect wires from a point of construction of the vehicle in some kinds of vehicles, as well as it requires much expense for the user. Moreover, there is a possibility to cause malfunction of engine control unit 3 at wiring work.